1. Field of the Invention
The present invention relates to an optical scanning device that can be used for laser beam printers, laser facsimiles, and digital copiers, for example. Further, the present invention relates to an image forming apparatus provided with such an optical scanning device.
2. Description of Related Art
Conventionally, as an optical scanning device of this type, a device is known which simultaneously scans four different photosensitive drums by combining two optical systems in each of which one polygon mirror (rotary polygon mirror) deflects laser beams from two semiconductor lasers serving as light sources such that two different photosensitive drums are scanned (see JP S58-95361A, for example).
Furthermore, in thus configured optical scanning devices, four optical detectors for determining a timing to start exposure are necessary for the laser beams, but a configuration has been proposed in which the number of components is reduced by providing only one optical detector for each polygon mirror in order to reduce the cost (see JP 2003-200609A, for example).
The optical scanning device disclosed in JP 2003-200609A is provided with a laser beam detector that is disposed on a scanning path of the first laser beam, and that outputs a signal indicating the detection of a beam when the laser beam is input, a horizontal synchronization signal generator for generating a horizontal synchronization signal serving as a reference when determining a timing to output an image of the first laser beam, by inputting the signal from the laser beam detector, and a second laser beam timing signal generator for generating a signal determining a timing to output an image of the second laser beam, by inputting and delaying, for a predetermined time, the horizontal synchronization signal of the first laser beam.
Thus configured optical scanning devices have an advantage, for example, that components such as reflecting mirrors can be reduced and that the degree of freedom in arrangement (i.e. in design) is relatively high.
However, two polygon mirrors as optical deflectors are used in thus configured optical scanning devices, so that it is necessary to use two polygon motors as rotatively driving devices, resulting in the problem that vibrations are more severer than those in optical scanning devices with one polygon motor.
Therefore, a new technique has been required that reduces vibrations in an optical scanning device using two polygon mirrors.